1. Field of the Invention
The invention relates in general to a digital-to-analog converter, and more particularly to a digital-to-analog converter capable of saving the circuit area.
2. Description of the Related Art
FIG. 1 shows a conventional digital-to-analog converter (DAC). The digital-to-analog converter is for converting a digital signal into an output analog voltage. In FIG. 1, the conventional digital-to-analog converter 100 includes a resistor string 110, which contains a number of resistors serially connected, and a select unit 120. The resistor string 120 generates a group of reference voltages between a high reference voltage and a low reference voltage. The select unit 120 then selects one reference voltage out of the group of the reference voltage as the output analog voltage Vo according to the digital signal Sd. However, when the digital signal Sd is increased by N bits, the amount of the resistors in the resistor string 110 grows 2N times accordingly in order to generate sufficiently fine output analog voltage. For example, when the digital signal is increased only by one bit, the amount of the resistors has to be doubled. Therefore, the more bit the digital signal has, the much greater amount of resistors are needed. Consequently not only the circuit area, but also the cost of the conventional DAC grows significantly.